[FFmpeg-devel] [PATCH v4 2/7] doc/indevs: Add example using cropping to capture part of a plane

Mark Thompson sw at jkqxz.net
Wed Apr 10 01:07:25 EEST 2019

 doc/indevs.texi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 1d5ed65773..a4f0f608d7 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -910,6 +910,14 @@ Capture from CRTC ID 42 at 60fps, map the result to VAAPI, convert to NV12 and e
 ffmpeg -crtc_id 42 -framerate 60 -f kmsgrab -i - -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12' -c:v h264_vaapi output.mp4
 @end example
+ at item
+To capture only part of a plane the output can be cropped - this can be used to capture
+a single window, as long as it has a known absolute position.  For example, to capture
+and encode the middle quarter of a 1920x1080 plane:
+ at example
+ffmpeg -f kmsgrab -i - -vf 'hwmap=derive_device=vaapi,crop=960:540:480:270,scale_vaapi=960:540:nv12' -c:v h264_vaapi output.mp4
+ at end example
 @end itemize
 @section lavfi

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